1. Field of the Invention
The present invention relates to a semiconductor device having a plurality of pixels arranged in matrix, which displays images with a video signal (also referred to as an image signal or a picture signal) input to each of the plurality of pixels, and a driving method thereof. In particular, the invention relates to a semiconductor device having a function of detecting and compensating defective pixels which would be caused in each column, and a driving method thereof.
2. Description of the Related Art
A driving method is proposed, by which gray scales capable of being displayed on a display screen are increased by providing a plurality of sub-pixels in one pixel (Reference 1: Japanese Patent Laid-Open No. Hei11-73158). For example, in Reference 1, one pixel is constructed from a pluraliuty of sub-pixels, thereby a gray scale which can be expressed with only light emission and non-light emission of one sub-pixel (hereinafter also referred to as a time gray scale method) can be combined with a gray scale which can be expressed with only a combination of the plurality of sub-pixels (hereinafter also referred to as an area gray scale method, and such a combination is hereinafter also referred to as an area/time gray scale method). Thus, the pixel disclosed in Reference 1 can increase gray scales which can be expressed with the area/time gray scale method.
There is also a driving method proposed, by which the characteristics of a light-emitting element in each pixel are detected to compensate degradation of the light-emitting element. For example, there are such a display device and driving method proposed that, if there is any degraded light-emitting pixel as a result of detection of the characteristics of a light-emitting element in each pixel, the luminance of the light-emitting element is compensated with a video signal input to each pixel, thereby compensating image burn-in (ghosting) or the like which is caused by changes in the characteristics of the light-emitting element (Reference 2: Japanese Patent Laid-Open No. 2003-195813).
However, in the conventional driving method of a pixel configuration where one pixel has a plurality of sub-pixels, there has been a problem in that if pixels have defects before shipment, any particular measures cannot be taken, which results in a lower yield. Further, even when pixels have defects after the display device starts to be used, any particular measures cannot be taken.